<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>过渡与动画</title>
    <style>
        div{
            font-family: Arial;
            font-size: 72px;
            font-weight: bold;
            position: fixed;
            left: 0;
            right:0;
            width: 30px;
            height: 30px;
            margin:auto;
            transform: rotate(90deg);  
            animation-iteration-count: infinite ;
            animation-direction: alternate-reverse ;
        }
    </style>
</head>
<body>
    <div>&gt;</div>
</body>
</html>